Zend_Cache_Frontend_Page

First of all there are several things to know about Zend Framework and caching. Whenever you work on a big web application caching is one of the mostly used mechanisms of speeding up the app and improve user performance. In general the task and the solution are pretty simple and natural.

As the application grows up the visitors become more and more impatient about what they receive. A single page is becoming slower and slower and the result is painful. First of all every time a user hits a page the application server uses the web server, a script interpreter, a database server and potentially the file system. But that’s not all. After all this output is generated on the server, as HTML in the most cases, it is sent to the client where again CSS and JavaScript engines parse and execute them.

In this scenario it’s easy to imagine how many time is spent. While there are several techniques to optimize the client side by optimizing JavaScript, CSS and the static images used for the design of the site, here I’m going to talk more about the backend.

Beside the Optimization

Let’s assume we’ve one of the very used combination between Apache (as a webserver), PHP (as server scripting language) and MySQL (as database server). Here you can choose to optimize all three of them. However beside the optimization of them one of the most simple steps you can do is to cache the output generated by these three branches of your web app.

Caching the Content

In fact you can cache only single parts of the whole process. For instance you can cache only the result returned by some slow database query. Let’s imagine a query takes about 2 seconds to execute. Now you can cache the result into a file and during the cache is active, i.e. it has not expired, the application takes it from a file stored somewhere in the file system.

In a typical Zend Framework scenario you can first setup the frontend and backend options of the cache.

$frontendOptions = array(
	'lifetime'                => 600, // in seconds - this is 10 seconds
	'automatic_serialization' => true,
);
$backendOptions = array('cache_dir' => 'cache/');
$cache = Zend_Cache::factory('Core', 'File', $frontendOptions, $backendOptions);
 
$cacheKey = md5('mykey');
 
if (!$cache->load($cacheKey)) {
	$slowQueryResult = $article->fetchAll();
	$cache->save($slowQueryResult, $cacheKey);
} else {
	$slowQueryResult = $cache->load($cacheKey);
}

You can setup different options here by setting up the cache directory, lifetime, etc.

Note that the cache directory must exists and with write permissions and Zend Framework doesn’t create it for you and will throw error.

The problem here is that now you cache only part of the generated content and in many cases this is still too slow for most of the users. However all the work (in most of the cases) of the web server, the script interpreter and the database server result in a simple HTML output. What if you have this output generated or cached for you and when the user hit the page the server will return this pre-generated code?

This is indeed very fast, because it’s similar to return a text file, as the HTML is simply formatted text.

Caching the Entire Page

Before I proceed, I’d like to say that I work with Zend Framework 1.9.x. Now in the latest versions of ZF there are new mechanisms of caching the output even Zend_Cache_Frontend_Page works fine on them.

You can simply setup the page cache within few simple lines of code:

$fo = array(
    'lifetime' => 600,
    'regexps' => array(
        '^/' => array(
	'cache' => true,
         'cache_with_cookie_variables' => true,
        ),
    )
);
 
$bo = array(
    'cache_dir' => 'cache/'
);
 
$cache = Zend_Cache::factory('Page', 'File', $fo, $bo);
$cache->start();

However my advise is to place this code as high as possible, because this will cache everything generated as output. It’s a good practice if you place this even in the bootstrap before you make the connection with the database. Actually you don’t need a database connection when you’ve to return a simple text(html) file.

This will improve your app’s performance a lot!

However there are few things to know. When you setup the cache to work even with cookie variables, you can see that hitting the page with different browsers Zend Framework will generated different cache pages. This is quite useless because than you don’t have any benefit of caching the content.

First of all let me say that THIS IS NOT A BUG! of ZF. Simply the framework will use the cookie variables to generate the cache key. It’s obvious that different browsers, even more different users, will have different cookie set and the framework will generate different cache keys for them.

Thus you’ve to change the setting to generate the cache key from cookie variable by explicitly set this option to false:

$fo = array(
    'lifetime' => 600,
    'regexps' => array(
        '^/' => array(
		 'cache' => true,
         'cache_with_cookie_variables' => true,
         'make_id_with_cookie_variables' => false,
        ),
    )
);
 
$bo = array(
    'cache_dir' => 'cache/'
);
 
$cache = Zend_Cache::factory('Page', 'File', $fo, $bo);
$cache->start();

Note that in this example we cache every single page generated by the framework explained in the regexps. This is not so good especially when the users have the possibility to login and to see customized content for them, so you can be careful what you cache.

A typical problem that this solution solves is when your application uses Google Analytics. As you may know Google Analytics sets up a cookie every time when an user hits the page, so every time the framework will generate a different cache for him and in result he won’t see any benefit and performance improvement from your site.